Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

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To the Editor:

In the article by Edvardsen et al1 in CHEST (July 2013), the authors discuss why mean maximal oxygen uptake (V˙o2max) in their sample (N = 759) is 9% lower compared with the HUNT Fitness Study (N = 4,631). The main point made by the authors is that a validation study on one portable MetaMax III X analyzer has been shown to give 8% higher oxygen uptake values than the Douglas bag system.2 As clearly described in several publications from our group, the portable MetaMax II analyzer was used in the HUNT study.3,4 Hence, we find the reference paper and the speculation made by the authors irrelevant for explaining the differences. Moreover, all MetaMax II analyzers used in the HUNT study were tested and found valid, against both Douglas bag and an iron lung, before being approved for use in the study. The validation and the reliability procedures are described in detail in a study by Loe et al.4

A more fruitful approach for a discussion across population samples may be to start with sample characteristics, as the two studies seem to have different recruitment strategies. The 4,631 subjects in the HUNT study were invited from 12,609 healthy subjects within three preselected municipalities and had to be free from cancer, obstructive lung disease, and cardiovascular disease; not using BP medication; and pass a brief medical interview to be eligible.3 In the study by Edvardsen et al,1 904 subjects met at the laboratory out of 1,930 randomly selected subjects from a base population of 3,485 participants described in Hansen et al.5 Despite that a high percentage of the base population report severe diseases, such as asthma (9%), cardiovascular diseases (5%), cancer (5%), and type 2 diabetes (3%),5 only 18 subjects (2%) were excluded from V˙o2max testing because of poor health condition.1 Hence, we question that the health status of the sample in the article by Edvardsen et al1 is comparable to the HUNT study. Additionally, a higher mean maximal heart rate (approximately 6 beats/min) in the HUNT study and potential differences in physical activity level may well explain the reported differences in V˙o2max.1,3,4

Comparison of physiologic variables across population samples is in itself a complex task. We strongly encourage the authors to discuss the uniqueness of each population sample when making comparison between studies, rather than making assumptions and conclusions based on other researchers’ equipment.

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